Over twenty-five years ago, a method of using a pulse signal to actuate a valve was introduced to control the flow rate and fluid pressure of liquids through a spray nozzle. Since then, this technique has remained largely the same or unused because it results in spotty spray patterns due to long dead times, which creates problems in an agricultural setting (e.g. crops, plants, trees, vegetables, winery), where sprayers are used to apply nutrients, herbicides, insecticides and water. In manufacturing settings, sprayers are used to apply coatings of paint colors and layers of chemicals, and ink on surfaces (e.g. plastic, paper, semiconductors, metals, and so on).
When pulse signals have been used to control the spray of fluids, the ejection of fluid from conventional single nozzles has been controlled by a single signal pulse stream. The voltage polarity of the signal pulse may be arbitrarily selected so that when the pulse is at a logic-HIGH value, then liquid is dispersed by the nozzle, and when the pulse is at a low value, no liquid is dispersed. The ON state is arbitrarily chosen to refer to when liquid is propelled or ejected, and the OFF state to no liquid. The duration of the ON or OFF pulse can be varied (PWM, pulse width modulated) to generate an average flow rate, to vary the flow rate and to control the droplet size.
In many settings, not just a single but multiple nozzles are used together. Sprayer systems have multiple nozzle bodies or outlets to apply liquids over a large or intricate surface area. Sometimes the activity of more than one hundred nozzles is coordinated, which makes PWM control complex.